HOUSTON — For the first time since the Gulf oil spill disaster started on April 20, the entire flow of oil was being contained Thursday as part of BP's pressure testing of a new cap, BP and federal officials said.

President Barack Obama called the news a "positive sign" but cautioned that "we're still in the testing phase."

If the cap holds, the idea is to keep it on — and the flow checked — until a relief well can plug the blownout well in August.